1. Technical Field This invention relates generally to improved systems for pumping semi-fluids, and particularly to computer controlled positive displacement pumps utilized in dispensing medicine and food products of various viscosity.
2. Background Art
Positive displacement pumps and motors using shutters for various valving functions are well known. Examples of such pumps include:
Bordini, in U.S. Pat. No. 4,759,695, describes a pumping unit for the filling of foodstuffs in containers in packaging machines. The conical shutter of the pumping unit, selectively connecting the pumping piston to the product intake duct and to the product delivery duct, is movable backwards from its seat.
In U.S. Pat. No. 5,141,408, Conrad et al disclose a product pumping device in which a dual piston alternately reciprocating pumping apparatus uses a precompression stroke. A reciprocating shutter plate is positioned between each feed cylinder and the hopper to regulate flow into the feed cylinders in a timed fashion. These shutter plates function as an intake valve for the feed cylinders. Separate discharge outlets positioned in the upper portion of each feed cylinder are not directly closed at any time during operation.
Garcia, in U.S. Pat. No. 5,186,368, describes a shutter for the outlet channel of a dispenser head for semi-liquid substances. The shutter is made of a resiliently deformable material and is engaged in a housing provided in the dispenser head so that the slot communicates with the outlet channel, and the head is in sealed contact with a portion of the inside surface as well as at least one side of the shutter side wall.
While development of such devices has continued, they nevertheless have various limitations relating to complexity, reliability, cost, and ease of manufacture, particularly in such devices to be used for food or medicinal dispensing.